Antarctica's McMurdo Dry Valleys may appear to be one of the least hospitable places on Earth. They contain a frigid desert where high winds scour the rocky ground, and the only water present is in the form of ice, some of it left over from when the ocean extended into the valley over a million years ago. The area is so inhospitable that NASA has used it to simulate conditions on Mars.

So biologists were probably very surprised to find that the area hosts a number of distinct ecosystems. Not on the surface; instead, these communities of bacteria live under the ice, in salty lakes that have been isolated from any external sources of energy or chemicals for anywhere from thousands to millions of years. Now, researchers have characterized one of the youngest under-ice lakes, which evidence suggests has been isolated from the air for only a few thousand years. Though estimates would suggest that the bacterial community within should be rapidly running out of food, the contents of the lake water suggest that the organisms are doing just fine, powered by the chemistry of the underlying minerals.

The most dramatic feature of the McMurdo Dry Valleys is probably Blood Falls, where iron both stains the ice red and helps power a community of bacteria that have been trapped within it for about 1.8 million years, ever since an arm of the ocean got cut off and frozen under a glacier. Lake Vida is in a different valley, and probably hasn't been isolated for nearly that long. It's extremely salty, and stays at a chilly -12°C under a sheet of ice that's at least 16m (52.8 feet) thick. But radiocarbon dating seems to indicate that it hasn't been isolated for nearly as long, and probably has exchanged carbon with the atmosphere within the last few thousand years.

Based on energy budget calculations, the authors expected that any communities trapped under the ice would be in what they called the "final steps of decomposition." The few microbes left should be feeding on the last remaining organic compounds and releasing methane in the process.

Sampling the water, however, showed that nothing of the sort was going on. Lake Vida's waters are anoxic (normally a condition that methanogens prefer), but are rich in dissolved organic compounds, including plenty of carbohydrates but little methane. There are also significant amounts of dissolved hydrogen in the waters. Nitrogen compounds were also very common, with supersaturated levels of nitrous oxide and high levels of ammonia. This mix of oxidized and reduced compounds suggested that the chemistry of the lake water was nowhere near the final steps of decomposition.

So, what's living in this complex mix? The authors looked for DNA sequences that help identify species, and found 32 of them from eight different phyla of bacteria. That is a broad enough sampling that it's hard to tell what, exactly, is likely to be powering the metabolism of most of them. However, it is a further indication that methanogens probably aren't dominating the system. It also showed that archaea, which are often common in extreme environments, are completely absent.

Based on the chemicals present in the brine of Lake Vida, the authors speculate that the bacterial community is powered by molecular hydrogen that can be released by a reaction between water and iron silicates in the underlying rocks. That hydrogen could then be incorporated into the complex organic compounds seen in the lake's waters.

If that's accurate, then it suggests that Lake Vida's life is probably powered by a different source of chemical energy than the one that sustains the life under the ice in a nearby valley (the one that creates Blood Falls).

That's a rather important finding, since it suggests that a diversity of simple, naturally occurring chemical reactions could provide the energy needed to sustain life, even in the absence of things like sunlight or plate tectonics. This in turn should influence our thinking about the prospects for finding life in the sub-ice oceans of places like Europa, as well as in possible sub-surface brines on Mars.

The other intriguing prospect is that the different dry valleys could all host distinct ecosystems, with different degrees of isolation and different sources of chemical energy. By sampling a few of them, we could potentially get a greater indication of how these communities could evolve over time. This may tell us something about life on our own planet, where communities appear to have survived several instances of global glaciations that created a "snowball Earth."

Perhaps a journalistic note, but are we really surprised by this anymore? I agree that studying unique ecosystems have value, but why are we "very surprised" that life flourishes in these circumstances? The earth (and probably by extension the cosmos) is fecund, not sterile.

Perhaps a journalistic note, but are we really surprised by this anymore? I agree that studying unique ecosystems have value, but why are we "very surprised" that life flourishes in these circumstances? The earth (and probably by extension the cosmos) is fecund, not sterile.

It sounds like a big part of it is that there are a number of isolated ecosystems that have evolved differently and use different energy sources despite being in such close proximity (and in the same relatively hostile environment).

That's a rather important finding, since it suggests that a diversity of simple, naturally occurring chemical reactions could provide the energy needed to sustain life, even in the absence of things like sunlight or plate tectonics.

Already known from the life surrounding deep-sea volcanic vents, right?

That's a rather important finding, since it suggests that a diversity of simple, naturally occurring chemical reactions could provide the energy needed to sustain life, even in the absence of things like sunlight or plate tectonics.

Already known from the life surrounding deep-sea volcanic vents, right?

Perhaps a journalistic note, but are we really surprised by this anymore? I agree that studying unique ecosystems have value, but why are we "very surprised" that life flourishes in these circumstances? The earth (and probably by extension the cosmos) is fecund, not sterile.

Living organisms that thrive in environments like that are not life as we know it, hence the surprise.

On another note, humor and sarcasm aside, it's nice to see another confirmation of the adaptability and ubiquity of life on earth. And I agree about the increased hope/chances for life on places like Europa.

Interesting as it is, one should distinguish between habitability for an established cellular biosphere and an environment that allows for a transition to one. These types of results are highly valuable for the former, especially as regards mass extinctions in general and the last refugias for a vanishing biosphere as a star and/or planet ages.

While we can't exclude environments as potentially transitional, we can tentatively identify the most likely.

If we go top down, phylogenies shows that early cells were RNA/protein based and before that RNA exclusively. They were also chemoautotrophs, consistent with an initial lack of much biomass and need for an environmental carbon source, as well as the relative complexity of organic photosynthesis.

It is possible that RNA polymers is the only nucleotide heteromer that works for thermodynamic reasons. But even if not it tells us about beneficial conditions on the primordial environment.

RNA heteromers are not so proficient enzymes as amino acid heteromers. But they too benefits from utilizing metals, and they are generally at least an order of magnitude better under anoxic conditions.

In conclusion, early cells profited from a hot, reducing, anoxic, metal rich, environment with redox sources driving their metabolism.

Going instead bottom up, the most abiotic productive environments are reducing ones with at least 3 orders of magnitude higher production rate of organics. This is vital since many suggested pathways to life crucially depends on enough concentration of organics.

Metal and heat promotes many synthesis pathways. On the other hand oxygen prevents many organics pathways or attack their products.

There is also a chemical selection for enthalpic enzymes as an environment cools. Those include RNAs already at the monomer level, such as say ATP coenzymes.

In conclusion, early organics production profited from a hot, reducing, anoxic, metal rich environment with redox sources driving it.

Are for example ice moons hopeless then, with relatively cold and vast, chemically dilute oceans, at cases alkaline conditions and over time diffusion or convection driven oxygen from UV catalysis of sunlit parts of the ice surface?

Likely no. Hydrothermal vents are ideal local environments as they have all* what is required up to reducing crustal volumes in a redox cycle. They also helpfully have thermal gradients that allows for optimal conditions and thermal cycling of many kinds of reactions.

Once life "takes" locally its evolution will spread it and they can inhabit extreme environments as the article tells us.

* With the possible exception of phosphorous. We likely got it from hydrothermal vents placed over subducting plates. However, I would guess smaller bodies have their own phosphor sources, the smaller the body the thinner the crust down to the minerals containing it.

And we have an increased contribution of local minerals by impactors. So I don't think this is a forbidding problem.

That's a rather important finding, since it suggests that a diversity of simple, naturally occurring chemical reactions could provide the energy needed to sustain life, even in the absence of things like sunlight or plate tectonics.

Already known from the life surrounding deep-sea volcanic vents, right?

Note that hydrothermal vent life in many cases may well be using energetics of photosynthesis indirectly, as they live with an oxygen rich environment. Anoxic conditions doesn't have as much available redox energy.

For example the giant tube worm are entirely living of the products of sulfur utilizing bacteria, so they are partway oxygen independent that way. They do have oxygen dependent mitochondria in their own cells though.

"They are remarkable in that they have no digestive tract, but the bacteria (which may make up half of a worm's body weight) turn oxygen, hydrogen sulfide, carbon dioxide, etc. into organic molecules on which their host worms feed. This process, known as chemosynthesis, was first recognized by Colleen Cavanaugh while she was a graduate student.[2]

The bright red color of the plume structures results from several extraordinarily complex hemoglobins found in them, which contain up to 144 globin chains (presumably each including associated heme structures). These tube worm hemoglobins are remarkable for carrying oxygen in the presence of sulfide, without being completely "poisoned" or inhibited by this molecule, as hemoglobins in most other species are.[3][4]"

In fact, the largest known complex multicellulars that live in fully anoxic conditions are only up to 1 mm large, but they manage a head and neural system as well as digestive system. Sediment living Loricifera: http://en.wikipedia.org/wiki/Loricifera . They rely on hydrogenosomes, mitochondria converted to utilize hydrogen instead of oxygen.

Presumably complex life can evolve directly towards utilizing lesser redox sources than those that include oxygen. But whales are a lot bigger organism to swallow. =D

Europa specifically is believed to have plenty of oxygen though. It is supplied by UV light photolyzing the sun lit ice surfaces and convected over about a million year down to the ocean.

Irrelevant, observation and testing is what theory lives on. A theory always knows more than our observations do, it is after all what it is constructed to do. The question is how much, and which theory knows most.

So the ability to make observations will always go towards making us trust scientific theory ever more, regardless of the specific outcome. Ref: "Science. It works, bitches." http://xkcd.com/54/ . (Except of course the global observation that theory doesn't work. That train has left the station, however, and likely it won't run off tracks as long as we can do observation at all.)

I don't think anyone has a specific theory what type of extreme environments extremophiles can inhabit though. Hence the surprises.

For example, even the observation that cells can survive temperatures above the boiling point of water at the surface is retrospectively unsurprising. The water doesn't boil under _those_ pressurized conditions the extremophiles live in.